<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    let num = +prompt('请输入一个整数:')
    // num > 10 ? alert(`${num}`) : alert(`0${num}`)
    num = num > 10 ? num : '0' + num
    alert(num)
  </script>
</body>

</html>